The former city centre home of the Birmingham Post & Mail has been placed on the market as plans are brought forward for the second phase of the mixed-use project.
Developer Chatham Billingham has commissioned consultancy CBRE to market the entire site and find either an outright buyer or a partner to work jointly on finishing the project.
The first phase of the development, in Weaman Street, comprises a 752-space car and 31,600 sq ft of offices and retail units and is due for completion later this year.
New plans have now been lodged with Birmingham City Council for the second phase of the project, called 'Post & Mail', to build a 14-storey tower on top containing office and residential accommodation.
Alan Chatham and Mark Billingham unveiled their plans for the former offices and printing works of the Post & Mail and Sunday Mercury in 2011 after the newspapers moved to Fort Dunlop in Castle Bromwich in 2008.
Their marketing brochure said: "Post & Mail provides a rare opportunity to acquire a significant new-build mixed-use building in the UK's second city, with planning consent to add a further 430,560 sq ft of office and residential space.
"A purchaser is sought to complete the project.
"The purchaser can acquire the existing interests and complete the development or alternatively participate within a joint venture through to a purchase of the asset upon practical completion.
"Chatham Billingham has appointed CBRE to identify a party to purchase phase one then work with them to complete the project and open Post & Mail as envisaged."
The original Post & Mail building was designed by renowned Birmingham architect John Madin and completed in 1964.
It previously had an imposing tower which was demolished in 2005 and replaced with Colmore Plaza while the remainder of the site opposite the West Midlands Police HQ was acquired by Chatham Billingham in summer 2009.
It also started The Cube before it was hit by financial problems.
The second phase of the Post & Mail project comprises plans for 245,630 sq ft of grade A office accommodation across seven floors and a further seven levels above containing 115 flats, including ten penthouse apartments.
Mailbox-based architecture firm Associated Architects said in a design statement: "The proposed mix of uses within the Post & Mail building has been carefully considered to ensure the development will complement and enhance the existing mix of uses within the Colmore business district which is predominantly focused on high-density office accommodation.
"The original brief for the building included some hotel use. Further investigation has proved that this is not viable.
"Whilst it is acknowledged residential use is currently limited within the Colmore business district, the potential for introducing high-quality provision into the area has been identified.
"The residential component of the Post & Mail development will also complement the future provision of housing within the existing Birmingham Children's Hospital site, as envisaged by the recently released Snow Hill Masterplan document."